Optically corrected helmet mounted display

Abstract

The present invention eliminates the relay lens systems found in conventional helmet mounted displays (HMDs) by removing field distortions and aberrations with a contoured fiber optic faceplate placed in close proximity to a liquid crystal display (LCD) or cathode ray tube. The optical system typically consists of a spherical dielectric or holographically made collimator-combiner, a dielectric or holographically made fold mirror, and a contoured fiber optic faceplate. The fold mirror is flat, and the collimator-combiner is made by coating a spherical eye glass blank. The system is configured as a folded and tilted catadioptric projector with the novel feature being the contoured faceplate. There are no dispersive elements in the imaging assembly which means it can be completely polychromatic (full color) without the need for additional color correction optics as found in all refractive color systems. When designed for full color, highest brightness, and see through capability it must be made with two or three narrow spectral and angular sensitive coatings on the fold mirror and on the collimator-combiner. These coatings allow the use of a tilt of the collimator-combiner with respect to the fold mirror which induces a small amount of astigmatism and keystone distortion but at the same time allows image light to pass through the folded optics to the eye with a minimum of loss. The elimination of a corrective refractive lens relay system makes this design polychromatic, less expensive, and lighter in weight, compared to a similar system with an achromatized and corrected refractive lens.

I claim: 
     
       1. An optically corrected helmet mounted display, comprising: a reflective collimator-combiner situated to combine with light rays from the surrounding environment a generated image and to transmit such combined image and light rays to the eye position;   a fiber optic faceplate located to receive an image from an image generator, said fiber optic faceplate having an input numerical aperture approximately equal to twice the pixel size of the image generator divided by the distance between said fiber optic faceplate and said pixels and having its output surface shaped to match the locus of points generated by ray tracing many parallel bundles of rays from the eye position to the points where the collimator-combiner focuses said parallel bundles of rays; and   a fold mirror placed to receive from the output of the fiber optic faceplate the generated image and to reflect such image to said collimator-combiner.   
     
     
       2. An optically corrected helmet mounted display, comprising: a reflective collimator-combiner situated to combine with light rays from the surrounding environment a generated image and to transmit such combined image and light rays to the eye position;   a first fiber optic faceplate located to receive an image from an image generator, said first fiber optic faceplate having an input numerical aperture approximately equal to twice the pixel size of the image generator divided by the distance between said fiber optic faceplate and said pixels;   a second fiber optic faceplate located in contact with the first fiber optic faceplate, said second fiber optic faceplate having smaller fibers with a higher output numerical aperture than the input numerical aperture of the larger fibers of said first fiber optic faceplate, to receive the generated image from said first fiber optic faceplate; the output surface of said second fiber optic faceplate having been shaped to match the locus of points generated by ray tracing many parallel bundles of rays from the eye position to the points where the collimator-combiner focuses said parallel bundles of rays; the output surface of said second fiber optic faceplate having been ground finer to increase the angle at which it will scatter light; and the output surface of said second fiber optic faceplate having been oriented at an angle with respect to the direction of the fibers in said second fiber optic faceplate such that the energy window will be directed to the desired eye position; and   a fold mirror placed to receive from the output of the second fiber optic faceplate the generated image and to reflect such image to said collimator-combiner.